1. Field of the Invention
The present invention relates to valves and, more particularly, to independently operated two stage valve assemblies for selectively restricting a flow of fluid under pressure.
2. Description of the Prior Art
In most machine shops, a machinist blows clean a work piece or blows shavings away from a piece of metal working machinery with an air gun connected to a source of air under pressure. These air guns have an on/off valve for controlling the flow of air through an attached nozzle; the flow rate of discharged air is primarily a function of the pressure of the air at it's source and the nozzle.
A high flow rate can cause severe problems in propelling the shavings at high speed or far enough to contaminate other equipment or work pieces. The safety of the machinist and other personnel may also be jeopardized by flying shavings, work pieces, etc. Moreover, delicate work pieces might be damaged by an impinging burst of air under high pressure.
For any given source of air under pressure, the maximum flow rate can be altered by substituting a different nozzle on the air gun. Such substitution, while permitting a broad range of discharge flow rates, is cumbersome, time consuming and seldom used in work environments wherein differing air flow rates may be desired interchangeably. To save time, some machinists and other operators have become quite skilled at operating the valve of an air gun to discharge a desired flow rate less than maximum; such skills take a long time to learn. Even so, skilled machinists do not always manage to regulate the conventional air gun sufficiently accurately to have a flow rate of the desired magnitude.
Various air guns, and the like, have been developed for a variety of purposes. U.S. Pat. No. 3,463,120 is directed to an electrostatic gun for discharging powder material, the discharge rate of which is regulated by one of two push buttons for operating respective microswitches. U.S. Pat. No. 3,986,523 is directed to means for sealing the valve assembly of a lever operated high pressure valve. U.S. Pat. Nos. 3,672,575 and 4,413,785 are directed to pressure guns having a secondary valve operated low pressure output. U.S. Pat. Nos. 2,783,092 and 3,129,892 disclose trigger and lever, respectively, operated air guns.